1. Field of the Invention
The present invention relates to an antenna device for transmitting or receiving radio waves to or from an aimed object, especially to improvements in an electronic scanning type array antenna device to be used in the field of radars or satellite communications.
2. Description of the Prior Art
FIG. 1 is a block diagram showing an example of a switching array antenna device which is an example of a constitution of a conventional electronic scanning type array antenna device; in the FIG. lij (i=1 to m, j=1 to n) is a number j antenna element in a number i electronic scanning type array antenna unit; 2.sub.ij (i=1 to m, j=1 to n) is a phase shifter for changing the phase of an exciting signal for the antenna element l.sub.ij ; 3.sub.i (i=1 to m) is an antenna element composition/distribution circuit for distributing an exciting signal to an antenna element l.sub.ij of a number i electronic scanning type array antenna unit or for composing the signals from the antenna elements l.sub.il -l.sub.in to form a receiving signal; 4.sub.i (i=1 to m) is an electronic scanning type array antenna unit comprising antenna elements l.sub.il -l.sub.in, phase shifters 2.sub.il -2.sub.in and an antenna element composition/distribution circuit 3.sub.i ; 6 is a plane selection circuit which selects one unit out of m units of electronic scanning type array antennas 4 and receives/transmits a signal from/to the selected unit; 8 is a control circuit which processes the phase shift quantities to be given to the phase shifters 2 to direct a radio beam to a desired direction, and executes selective control of the plane selection circuit 6; and 9 is an input/output terminal of signals.
A transmitting operation will be explained as an example of operations in the following. Upon processing information about the direction of a beam, the control circuit 8 selects one unit out of m units of electronic scanning type array antennas 4 with the plane selection circuit 6. A signal input to the input/output terminal 9 is transmitted to an antenna element composition/distribution circuit 3.sub.i of an electronic scanning type array antenna unit 4.sub.i selected by the plane selection circuit 6, and it is distributed to n antenna elements l.sub.il -l.sub.in by the antenna element composition/distribution circuit 3.sub.i and the distributed signals are radiated into the space from the antenna elements l.sub.il -l.sub.in. At this time, phase shift quantities .phi..sub.il -.phi..sub.in, expressed by the following equation (1), are given to phase shifters 2.sub.il -2.sub.in for individual antenna elements 1.sub.il -1.sub.in controlled by the control signal from the control circuit 8, and the signals radiated from the antenna elements 1.sub.il -1.sub.in are composed in the space to form a radio beam to be radiated in a desired direction. EQU .phi..sub.ij =(e.sub.p .multidot.e.sub.r)2.pi./.lambda.. . . (1)
where e.sub.p is a position vector expressing the position of an antenna element 1.sub.ij ; e.sub.r is a unit vector in the direction of the beam; (e.sub.p .multidot.e.sub.r) is an inner product of these two vectors; and .lambda. is a free-space wavelength of a radio wave to be radiated.
The electric field intensity E.sub.i (.theta., .phi.) is expressed by the equation (2) as shown below. ##EQU1##
where A.sub.j is the amplitude of an exciting signal which excites the number j antenna element 1.sub.ij with the antenna element composition/distribution circuit 3.sub.i, and g.sub.j (.theta., .phi.) expresses the directivity of number j antenna element 1.sub.ij.
The directivity of an antenna element g.sub.j (.theta., .phi.) is approximately expressed as an exponential function of cosines, and the amplitude becomes small at a large angle, so that the beam scanning angle of an electronic scanning type array antenna unit 4.sub.i is delimited; therefore when there is a need to scan a radio beam in a wide range such as the case of mobile communication, a plurality of electronic scanning type array antenna units 4.sub.l -4.sub.m are used to cover the necessary scanning range in a conventional electronic scanning type array antenna device as shown in FIG. 1.
FIG. 3 is an example showing the beam coverage in the case of mobile communication; in the FIG., 10.sub.i (i=1 to m) show individual beam coverages of m units of electronic scanning type array antennas 4; 12 shows a desired beam coverage. In the example shown in the figure, seven units of electronic scanning type array antenna units 4.sub.1 -4.sub.7 are needed to cover the desired beam coverage 12. In an example as shown in FIG. 4, the number of antenna elements 1 of an electronic scanning type array antenna unit is increased to widen the coverage and six units of electronic scanning type array antenna units 4.sub.1 -4.sub.6 are needed to cover the desired range. Usually, an electronic scanning type array antenna unit comprises several tens of antenna elements, and in some case it comprises thousands of antenna elements. When a wide range has to be covered as in the case of mobile communication, a plurality of antenna units as mentioned in the above are needed; therefore a large number of antenna elements 1 and a large number of phase shifters 2 are needed, as a result there occurs a problem that both weight and size of the device become large.